我有一个更新查询，我在其中明确引用了数据库，但 MySQL 仍然提示消息:ERROR 1046 (3D000): No database selected。

其他结构相似但使用 INSERT 的查询工作正常。其他仅执行 SELECT 的查询也运行良好。

要在测试用例中重复该问题，请尝试运行这些查询:

create table test.object1 (
    id_object1 int unsigned not null auto_increment,
    total int,
    weight int,
    dt datetime,
    primary key (id_object1)
) engine=InnoDB;

create table test.object2 (
    id_object2 int unsigned not null auto_increment,
    primary key (id_object2)
) engine=InnoDB;

create table test.score (
    id_object1 int unsigned not null,
    id_object2 int unsigned not null,
    dt datetime,
    score float,
    primary key (id_object1, id_object2),
    constraint fk_object1 foreign key (id_object1) references object1 (id_object1),
    constraint fk_object2 foreign key (id_object2) references object2 (id_object2)
) engine=InnoDB;

insert into test.object1 (id_object1, total, weight, dt) values (1, 0, 0, '2012-01-01 00:00:00');
insert into test.object1 (id_object1, total, weight, dt) values (2, 0, 0, '2012-01-02 00:00:00');

insert into test.object2 (id_object2) values (1);

insert into test.score (id_object1, id_object2, dt, score) values (1, 1, '2012-01-03 00:00:00', 10);
insert into test.score (id_object1, id_object2, dt, score) values (2, 1, '2012-01-04 00:00:00', 8);

update test.object1 p
join (
    select ur.id_object1, sum(ur.score * ur.weight) as total, count(*) as weight
    from ( 
        select lur.* 
        from ( 
            select s.id_object1, s.id_object2, s.dt, s.score, 1 as weight
            from test.score as s 
            join test.object1 as o1 using(id_object1) 
            where s.dt > o1.dt
            order by s.id_object1, s.id_object2, s.dt desc 
        ) as lur 
        group by lur.id_object2, lur.id_object1, date(lur.dt) 
        order by lur.id_object1, lur.id_object2 
    ) as ur 
    group by ur.id_object1
) as r using(id_object1) 
set 
    p.total = p.total + r.total, 
    p.weight = p.weight + r.weight, 
    p.dt = now();

注意:我在 PHP 环境中运行这些查询，并且我没有明确使用 mysql_select_db('test')，因为我不想这样做，而且其他(很多!)查询都不需要它。我确信使用 mysql_select_db 可以解决我的问题，但我想知道为什么这个特定查询不起作用。

为了比较:如果你运行这个更简单的查询，也不使用 mysql_select_db，一切正常:

update test.object1 set total=1, weight=1, dt=now() where id_object1=1;

我已经搜索无果。我发现的唯一接近的是这个错误报告:http://bugs.mysql.com/bug.php?id=28551尤其是最后一条(未回复的)消息...

最佳答案

您的字段命名不正确，但即使您更正了它们，这也是 MySQL 中的一个错误，如果您没有默认数据库，则不允许您这样做。

update  test.object1 p
join    (
        select  ur.id_object1, sum(ur.score * ur.weight) as total, count(*) as weight
        from    (
                select  lur.*
                from    (
                        select s.id_object1, s.id_object2, s.dt, s.score, 1 as weight
                        from   test.score as s
                        join   test.object1 as o1
                        using  (id_object1)
                        where  s.dt > o1.dt
                        order by
                               s.id_object1, s.id_object2, s.dt desc
                        ) as lur
                group by
                        lur.id_object1, lur.id_object1, date(lur.dt)
                order by
                        lur.id_object1, lur.id_object1
                ) as ur
        group by ur.id_object1
        ) as r
USING   (id_object1)
SET     p.total = p.total + r.total,
        p.weight = p.weight + r.weight,
        p.dt = now();

问题特定于具有双嵌套查询且没有默认数据库的UPDATE(SELECT 或单嵌套查询或默认数据库工作正常)

关于php - MySQL "ERROR 1046 (3D000): No database selected"更新查询，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10653577/